A spin transfer magnetic random access memory (MRAM) comprising, as a storage element, a magnetoresistive element with a ferromagnetic substance has been proposed. The MRAM is a memory that stores information by changing the direction of magnetization in a magnetic layer by a current transferred into the magnetoresistive element to control the electrical resistance of the magnetoresistive element between a high-resistance state and a low-resistance state.
The magnetoresistive element comprises a storage layer that is a ferromagnetic layer with a variable direction of magnetization, a reference layer that is a ferromagnetic layer with an invariable direction of magnetization, and a tunnel barrier layer that is a nonmagnetic layer formed between the storage layer and the reference layer. The tunnel barrier layer is formed of an oxide film, for example, MgO. In this case, the characteristics of the magnetoresistive element are affected depending on the distribution of concentration of oxygen (O) in the tunnel barrier layer (oxide film).